The invention relates to the field of radiometric imaging.
Radiometric imagers may use an active or passive scanning technique. Active imagers project electromagnetic radiation at an object and scan the reflected radiation with a detector. Spatial information of the scanned image may be produced by deflecting the electromagnetic radiation, moving the detector, or both. Passive imaging systems may create images using ambient radiation and radiation emitted from the object(s), such as using a staring detector array at the focal plane. Optionally, passive imaging systems use scanning technologies. As used herein the term detector refers to a sensor for a single image pixel, such as a detector of a scanning imager, a detector of a staring array, a detector of a line scanner, or the like.
Radiometric imagers may use calibration to improve computed images, such as improving accuracy of pixel values, reducing noise, correcting for aberrations, and/or the like. Calibration may be performed using an external image/object that may produce an image with known pixel values, and computationally correcting the measured pixel values to match the known ones. Calibration may be performed using an internal signal/radiation source that produces known pixel values, and computationally correcting the measured pixel values to match the known ones.
Passive imagers may use a Dicke switch, to switch between each array element and an inline resistance to ground. This may also be called a switchable resistance. For example, Dicke microwave radiometers determine the temperature of the microwave background radiation better than conventional radiometers, such as better calibrating high frequency signals. For example, Dicke switches are used to increase the accuracy and stability of calibrations, such as calibration of internal noise sources.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the figures.